1. Field of the Invention
The present invention relates to an apparatus for detecting an abnormality in a d.c. motor driving system. More particularly, the present invention relates to an abnormality detecting apparatus for detecting an abnormality in a direct current (d.c.) motor driving system including a d.c. motor and a driven apparatus, in which a switching element connected to the d.c. motor in series is provided in a power supply path extending from a driving power source to the d.c. motor and the rotation of the d.c. motor is controlled according to the switching control of the switching element, thereby driving the driven apparatus.
2. Related Art
Conventionally, it is known by unexamined Japanese Patent Laid-open Publication No. Sho 61-291225 to detect an abnormality in a throttle system by generating a pseudo motor drive signal to a motor driving circuit for rotating a d.c. motor forwardly or in reverse while the control of the d.c. motor for driving a throttle valve is cancelled and to detect a terminal voltage of the d.c. motor at that time.
It is also known by unexamined Japanese Patent Laid-open Publication No. Sho 7-4296 to monitor a terminal voltage of a d.c. motor which drives a throttle valve and to detect an abnormality in a throttle actuator on the basis of the terminal voltage, an upper limit value of the terminal voltage which is preset corresponding to an accelerator position and an accelerator position change rate, an accelerator position, and an accelerator position change rate.
The abnormality in the throttle system is caused by not only an abnormality in a throttle actuator system but also an abnormality in a controller system for controlling the d.c. motor for driving the throttle valve.
The abnormalities in the throttle actuator system may be a lock of the d.c. motor for driving the throttle valve, short-circuit of a coil, disconnection in the coil, lock of the throttle valve itself, lock of a gear connecting the d.c. motor and the throttle valve, idling of the d.c. motor due to disengagement of gears, and the like. The abnormalities in the controller system are an abnormality in the switching element as a component of the controller, an abnormality in the power supply path extending from the driving power source to the d.c. motor, and the like.
According to the above conventional system as disclosed in the publications Nos. 61-291225 and 7-4296, however, the abnormality in the throttle actuator system and that in the controller system cannot be distinguished from each other although the abnormality in the throttle system can be detected. Consequently, in case of analyzing the cause of the abnormality in the throttle system, both of the throttle actuator system and the controller system have to be checked. Thus, much time is required to analyze the cause of the abnormality.
With respect to not only the throttle system but also various apparatuses such as a fuel injection pump driving apparatus driven by a d.c. motor, it is required to detect an abnormality in the d.c. motor or a driven apparatus driven by the d.c. motor and an abnormality in a switching element for switching the d.c. motor or a power supply path extending from the driving power source to the d.c. motor while distinguishing those from each other.